angular.module('todoApp').factory('todoService', function() {
  const storage = 'sessionStorage';

  function save({ todoList, archivedList }) {
    window[storage].setItem('todoList', angular.toJson(todoList));
    window[storage].setItem('archivedList', angular.toJson(archivedList));
  }

  function query() {
    const todoList = window[storage].getItem('todoList');
    const archivedList = window[storage].getItem('archivedList');
    return {
      todoList: (todoList && angular.fromJson(todoList)) || [],
      archivedList:  (archivedList && angular.fromJson(archivedList)) || []
    };
  }
  
  return {
    save,
    query
  };
});